In 1987, C. W. Tang and Van Slyke of Eastman Kodak Company, USA, reported a breakthrough in organic electroluminescent research. A double-layer small-molecular organic electroluminescent device with high brightness and high efficiency was prepared by vacuum coating technology. In 1990, R. H. Friend group of the University of Cambridge prepared the first polymeric light-emitting diodes. Since then, Organic Light-Emitting Diode (OLED) has been developed to the application stage in less than twenty years.
However, the hole injection layer of the traditional organic electroluminescent device commonly employs small organic molecules, which may be susceptible to oxidation and may be unstable. This affects the service life and the efficiency of the organic electroluminescent device.